The present invention is directed to an igniter module for a vehicle supplemental restraint system, and more particularly to a igniter module that facilitates factory testing of a bridge element installed in the igniter module.
Vehicle supplemental restraint systems nearly always include restraints that are pyrotechnically deployed by supplying electrical current to a bridge element or squib. Obviously, system reliability requires electrical integrity of the bridge element and its connections to an associated deployment circuit, and various on-board diagnostic routines have been developed for periodically checking the bridge integrity by monitoring a bridge voltage developed in response to a small bridge current. However, there is a desire, particularly in the factory environment, to provide direct access to the bridge element of an assembled igniter module to enable more precise and/or extensive measurement of bridge element parameters such as electrical resistance and thermal capacitance. This is particularly difficult to achieve with a modular or integrated igniter that includes deployment circuitry designed for bus communication with a central control module. Direct access to the bridge element could be achieved, of course, by configuring the modular igniter package to include a pair of dedicated test terminals coupled to the internal bridge element, but this would significantly increase the cost of the igniter package. Accordingly, what is needed is a low cost modular igniter package having a mechanism that enables factory measurement of bridge element electrical parameters.
The present invention is directed to an improved and low cost modular igniter package designed for bus communication with a central control module, and having an internal bridge element that is electrically accessible for factory testing of the bridge element. According to the invention, temporary electrical interconnects internal to the igniter package electrically couple the bridge element to a pair of external bus communication terminals, enabling direct access to the bridge element by factory test equipment for accurate measurement of electrical parameters such as electrical resistance and thermal capacitance. Following measurement of the electrical parameters, the temporary interconnects are electrically destroyed, isolating the bus communication terminals from the bridge element. In a preferred embodiment, the temporary interconnects are formed by a pair of metal fuse elements, which are electrically destroyed by electrical currents passing through the fuse elements and respective diodes coupling the bridge element to a ground terminal of the igniter package.